With rising prices of bulk materials such as coal and iron ore, there is a rising demand on weighing accuracy of belt weighing devices for use on a belt conveyor. Meanwhile, reliability and stability of the weighing accuracy of the belt weighing devices are becoming more important. Weighing sensors and weighing control instruments currently used for belt weighing scales measured by belt conveyor may have high weighing accuracy of up to 0.03% or more. However, a belt weighing scale configured on a belt conveyor has an accuracy of only between 1% and 0.5% and the stability of the accuracy is often unsatisfied. This may be caused by various factors including belt tension variations and vibrations, depending on the amount of materials handled by the belt conveyor. This may also because the calibration cannot be easily and timely performed.
Existing calibration methods of a belt weighing scale include hanging weight calibration, chain code calibration, cycle chain code calibration, electronic calibration, and material calibration. Among them, the material calibration can substantially truly reflect the status of the materials on an operating belt conveyor, which provides a high level of calibration credibility. Other calibration methods are analog calibrations that cannot reflect the status of the belt tension when the materials cover the entire length of a belt conveyor, which have large calibration errors and thus cannot meet requirements in practice. On the other hand, the material calibration requires a material amount of at least about 2% of the conveying capacity of a belt conveyor according to the requirements of the national standards. When the conveying capacity of a belt conveyor is about 5000 tons per hour, the material amount required for performing the material calibration is about 100 tons per hour. As larger capacity conveyors (10,000 tons per hour) appear, the amount of materials required for the material calibration becomes larger, and thus equipment for material weighing becomes larger.
Existing material calibration methods use forms including a hopper weighing scale, a truck weighing scale, and a track weighing scale. Therefore, the cost for calibration equipment is high. Many steps are involved in taking and discharging materials onsite, and it is hard to obtain desired accuracy for the material calibration. In addition, such calibration affects a normal production process and cannot be timely performed. Further, such calibration takes a long time each time the calibration is performed, and the calibration cannot be easily performed.